Tonal quality. The regular “Bluesband” or “Marine Band” harmonica sounds “tinny-ish” for lack of a different word.
Listen to one of JP Allen’s lessons - he’s using the Special 20 while his student is using the Bluesband and when the student starts with whatever he’s practicing, listen to the difference in tone. His has a richer tone. I know it’s not just because he’s good, though he is! I know, too, because I got a Special 20 before I ordered his lesson not realizing I’d be getting one of the harmonicas he gives away to “aspiring” harpists. When the Bluesband came in I went right to playing along with a lesson and it just didn’t sound as rich (for lack of a better word) as the Special 20.
I am giving my Blues Band to my 2nd oldest grandson if he gets into it like he said he was going to after football season is over.
They aren’t bad harps, either one, tho I definitely prefer the Special 20 over the Blues Band tho when I get to the bending (am thinking about it for single notes too as I’m struggling with those along with bending but we’ll see on the bending part)
Hope that helped some. I’m a beginner and have JPs’ Happy Harpin’ lessons and i can just hear the tone on the Special 20 sounds so much richer than the BluesBand one.
Hopefully someone with more knowledgeable can help or try googling "What is the difference between the Marine Band and Special 20s. Also go to youtube and listen to some of his free lessons - just search JP Allen and pick any of the training vids and see for yourself. Maybe that’ll help, hearing the difference.
Other than the fact I was going for the Lennon instead of the Special 20 when I decided to stick with what JP suggested for beginners as the best for beginners AND intermediates AND he still uses his even on gigs.
So your call unless we can get some folks woke up enough to check the forums out because I’ve had a number of questions that haven’t been responded to. Not sure they keep up a lot with this section of the business. But there are some gurus here who do answer some questions but mostly don’t appear to.
Also try copying and pasting it somewhere it looks like there’s a ton of people in that forum group that answers questions more often
Good luck - can’t wait to hear your responses!!